Rotary tablet forming machines of the category-related type are known. A typical factor here is that, upon starting the drive unit, the rotor is brought from standstill position to its rated speed. By way of at least one filling shoe, the matrixes are filled with the press mass and, depending on the angular position of the rotor, the lower and the upper punches which are guided by guide curves are moved axially to the matrixes. The upper and lower punches are directed past at least one press station, normally a pre-press station and a main press station. At that location, the upper and lower punches are directed past stationary arranged press rollers, essentially tangential, so that a pressing force can be applied onto the press mass filled into the matrixes.
Setting and measuring the pressing force is known, for example from EP 0 698 481 B1. In this case, there is an essential correlation between the measured maximum pressing force and the mass of the press mass filled into the matrixes under the prerequisite of the same material properties of the press mass. There is, in this case, a direct correlation between the tablet weight and the pressing force required for the manufacture of the tablets. In dependence on the material to be pressed, a certain pressing force is allocated to each tablet weight with a tablet form pre-specified by the press tools and a set tablet height. If the filling volume, and subsequently the tablet weight, fluctuates at a constant tablet height, a pressing force change results therefrom in direct dependence.
If all matrixes in a rotary tablet forming machine are normally filled with press mass up to the press station (meaning, up to the pressure roller), pressure rollers and rotor during start-up are accelerated to the rated speed in the same time period. This is attributable to the fact that each punch, as a result of the rotational movement of the rotor, is drawn past under the pressure roller—touching this—and her via the rotation of the punches the acceleration of the pressure roller is effected so that the acceleration of the pressure roller is directly dependent on the rotational speed of the punches.
This correlation between acceleration of the rotor and acceleration of the pressure rollers is then disadvantageous if, upon rotation of the rotor, the matrixes arriving at the press station (pressure rollers) are not or are only partially filled with press mass.
This can be the case, for example, during the start-up of the rotary tablet forming machine after cleaning or in the event of an interruption of the material feed by way of the filling shoe(s) with press mass.
If the rotary tablet forming machine is now started up with non-filled or with only partially filled matrixes, the upper and lower punches in the press station do not touch or only partially touch the pressure rollers. By starting up the drive unit the rotor with the punch is, however, accelerated to its rated speed. If a first punch with a first orderly filled matrix now accesses the press station, the punch or the punch couple, corresponding to the rotor already accelerated to rated speed, hits the pressure roller which is not yet or only insufficiently accelerated. In this case, the punch has an abrupt impact on the pressure roller so that suddenly a high kinetic energy has to be absorbed by the pressure roller and the punches involved. This can lead to damage of the pressure rollers and/or the punches.